Protective coatings for use on numerous substrates are known in the prior art. For example, U.S. Pat. No. 5,296,288, the contents of which are incorporated herein by reference in its entirety, issued on Mar. 22, 1994 describes a protective coating for ceramic materials and a thermal control structure comprising a ceramic material having the protective coating thereon. The protective coating includes, in admixture, silicon dioxide powder, colloidal silicon dioxide, water and one or more emittance agent(s) selected from the group consisting of silicon tetraboride, silicon hexaboride, silicon carbide, molybdenum disilicide, tungsten disilicide, and zirconium diboride. The invention therein has the drawback that the coating must be used immediately after the composition is prepared.
Prior efforts have been made to generate protective coatings having high emissivity characteristics for use on metal surfaces. U.S. Pat. Nos. 5,668,072 ('072) and 6,007,873 ('873) issued respectively on Sep. 16, 1997 and Dec. 28, 1999 teaches a high emissivity coating composition, and methods of use for coating the interior of furnaces, in which the coating composition includes a high emissivity agent such as a rare earth oxide and a binder agent. The preferred emissivity agent is cerium oxide or related agents including mixed oxides of cerium oxide and precursors. Terbium may be substituted for cerium. The binder, which also is used as a suspension agent, includes an aluminum phosphate solution, peptized aluminum oxide monohydrate and ethyl alcohol. The inventions of '072 and '873 make use of organic substances potentially increasing the amount of fumes generated during heating.
U.S. Pat. No. 4,810,300 ('300) issued on Mar. 7, 1989 discloses a composition to produce an adherent and water insoluble deposit on substrate surfaces, which deposit is used for inks, paints and the like. The coating material for the substrate surfaces includes at least water, a pre-reacted lithium silicate and an unreacted lithium hydroxide monohydrate. Preferably, the liquid phase contains a dispersant in the form of clay. A suitable pigment or other refractory material such as graphite, oxides, borides, nitrides, carbides, sulfides, metals and mixtures thereof may also be incorporated therein. The effective temperature range of the coating material is up to about 2000° C. The '300 invention adheres to metal surfaces but does not provide thermal protection to the underlying surface.
U.S. Pat. No. 5,569,427 ('427) issued on Oct. 29, 1996 describes a high temperature coating for use on a ceramic substrate and a non-firing process for obtaining the high temperature coating. The coating comprises a silica taken from a silica sol, an alumina, a silicon carbide and a molybdenum disilicide. The coating has an operating temperature up to 1500° C. The coating of '427 is used immediately after being prepared, and is formulated for ceramic substrate surfaces.
U.S. Pat. No. 6,444,271 ('271) issued on Sep. 3, 2002 discloses a durable refractory ceramic coating having a silicide coating comprising a refractory metal and silicon, which combines to form a silicide. The coating described therein is at least partially diffused into the base structure of at least one surface. The base structure is a ceramic material, which is preferably a ceramic oxide material. The invention of '271 uses a polymeric stock solution for a carrier to apply the coating thereby potentially increasing the flammable nature of the stock solution.
It is also known to use bentonite in heat resistant coatings. U.S. Pat. No. 4,072,530 issued on Feb. 7, 1978 teaches a refractory furnace wall coating composition containing silicon carbide, a stabilized zirconium oxide or bentonite, a silicon dioxide, a hydrolyzate of poly(ethyl silicate), a sodium silicate or aluminum phosphate and water.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.